Portable computers and other electronic devices continue to be reduced in size as advances in technology reduce the size of components used to manufacture these devices. Along with this size reduction, compact slots have been provided in the devices for receiving integrated circuit (“IC”) cards. In an effort to standardize IC card formats, the Personal Computer Memory Card International Association (“PCMCIA”) has promulgated various standards governing the physical dimensions and interface configurations of IC cards (or PC cards). The PCMCIA standards set forth, among other things, IC card physical dimensions, electrical interface requirements between IC cards and the devices utilizing the IC cards, and a data format for the interchange of information between IC cards and devices utilizing IC cards. In addition to having 3 volt (130-150 mA) pins, PCMCIA slots (both standard size and “mini-PCMCIA” slots) may also have two 5-volt pins (each of which source 500 mA), which thereby limits the sourcing capability of the 5-volt pins to a total of 1 A at 5 volts.
Computer manufacturers have endorsed the PCMCIA standards and have included at least one slot for a PCMCIA card in virtually all laptop, sub-notebook and notebook computers. In response to the increasing popularity of the PCMCIA standards, numerous PCMCIA-compatible devices, such as hard drives, modems, local area network adaptors and wireless communication systems, have been developed. For example, one wireless communication card that serves the function of a wireless modem connectable to a cellular network is manufactured by Nokia under the product name “D211.” Sierra Wireless and others produce similar devices, referred to herein generically as “cellular IC cards.” Cellular functionality may also be integrated into combination cards that combine wireless LAN (WiFi) and cellular capability. Given these integration capabilities, the computer user may plug a card into his/her PC or laptop that provides wireless/cellular capability.
Unlike many applications that use PCMCIA or similar slots, however, cellular hardware can have very high peak current and/or power requirements that exceed the source capability of the PCMCIA slot for short periods of time. These peak current/power periods occur during transmit bursts or “pulses”, when the cellular power amplifier (PA) transmits at power levels of over 2-3 W and draws more than the total of 1 A at 5 V available from the slot. For example, GSM/GPRS transmission requires a current of approximately 2A for the pulse duration, which exceeds the amount of pulsed current that can be supplied by the PCMCIA.
In an attempt to an on-demand temporary power source for use during these high-consumption periods, capacitors have been employed that are charged by a low current during the interval between pulses and supply the pulse current to the transmitter. High capacitance is, however, needed to minimize voltage drop to minimize the conductive and emitted electromagnetic interference and increase transmitter output power and efficiency. Supercapacitors (double layer capacitor), for instance, have been used for this purpose. However, supercapacitors tend to exhibit a high equivalent series resistance (“ESR”), which may result in a higher voltage drop compared to other solutions with high capacitance but lower ESR. In addition, supercapacitors are not assembled using the reflow process, which limits their usage in an automated manufacturing line and increases the need for manual operation and cost of the assembly. Individual capacitors (e.g., tantalum) have also been connected in parallel on the board. Nevertheless, this complicates the assembly process, requires higher overall footprint space, and may the electrical circuit more sensitive to the influence of PCB parasitic resistance and inductance.
As such, a need currently exists for a relatively simple and inexpensive capacitor system that is able to better satisfy industry requirements regarding size and performance.